Generators are a type of electric machines used to produce electrical energy. Generator operation is based on the principle of electrical induction, whereby a periodic flow of electricity is produced in a loop-type conductor as a result of the periodic variation of the flux of the magnetic lines of force passing through the loop. To do this, either the loop is caused to rotate in a constant magnetic field or, alternatively, the magnetic field can be rotated. Thus, a gap is formed between the rotating element and the stationary element. Many generators cool the rotating and stationary elements by passing air through the gap between these components to increase life and efficiency of the generator. Many generators utilize air cooling in which a fan or pump is used to accelerate the air entering the gap. The use of fans and pumps add work to the air, increases the temperature of the air prior to entering the gap and hence, reduce the efficiency of the generator. Furthermore, overall efficiency will be lower because work will be required to run the fan or pump.
Several schemes have been used to cool generators and motors. For example, in U.S. Pat. No. 3,558,942 issued to Roger Gettys Hill et al. on Jan. 26, 1971, a motor is disclosed having an improved cooling means. The compressed air, from an external air compressor, is forced through circumferentially arrayed passages within the rotor whenever cooling is required.
Another cooling scheme is disclosed in U.S. Pat. No. 4,427,908 issued to Beza Halmal on Jan. 24, 1984. An electric machine has air under pressure which is circulated in a closed circuit. After the air is heated by the thermal losses of the electrical machine, the air is cooled in a heat exchanger and directed back into the machine.
Another cooling scheme is disclosed in U.S. Pat. No. 4,611,137 issued to Thomas Sutrina on Sep. 9, 1986. A machine is disclosed having a stator and a rotor forming an air gap. Grooves are provided to collect coolant under the influence of centrifugal force and a pilot pump collects coolant from the associated groove to convey the same to a pressure pump.
The solutions to the cooling problem, as mentioned above, complicate the structure, increase cost and complicate the system design used to cool generators and motors while attempting to increase efficiency.
The present invention is directed to overcoming one or more of the problems as set forth above.